HYPHOMYCETES 543 



oval spores. The spore-containing cell is known as an ascus and the 

 spore ascospore. 



Somewhat more complex is reproduction of the common green 

 mold, Aspergillus. An aerial hypha or conidiophore develops, thicker 

 at the distal than at the proximal end, and from this thickened end 

 radially arranged spherical or oval conidia arise. 



Microscopical Examination of Molds. Molds are usually best 

 examined in water, to which an equal volume of glycerin has been 

 added, and unstained. The general arrangement of mycelium, spores 

 and sexual bodies can be observed with the lower powers of the 

 microscope the finer details of structure require a greater magni- 

 fication. Anilin dyes color molds readily and the Weigert fibrin- 

 staining method is very good to demonstrate molds in tissue sections. 



FIG. 86. Penicillium ; conidiophores, sterigmata, and conidia. 



Growth on Artificial Media. Molds are almost invariably aerobic 

 and their development in artificial media requires abundant free 

 oxygen. A slightly acid reaction is best for their growth, but media 

 with an alkaline reaction and even a relatively strong acid reaction 

 (organic acids, not mineral acids), will usually permit of their mul- 

 tiplication. Even on very dry media development takes place. 



Pathogenic Molds. Favus. Favus or tinea favosa is a skin disease 

 limited chiefly to the hairy parts of the body; more frequently the 

 head alone is involved, but the disease may spread over the entire 

 surface of the body. It is not limited to man dogs, cats, mice and 

 rabbits are also susceptible. The disease is contagious and is trans- 

 mitted from man to man or from animal to man by contact. Unclean- 

 liness is a potent predisposing factor, but individuals with lowered 



